#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define LOG(FMT...) fprintf(stderr, FMT)

int exgcd(int a, int b, int &x, int &y) {
	if (b) {
		int d = exgcd(b, a % b, y, x);
		y -= a / b * x;
		return d;
	}
	x = y = 1;
	return a;
}

int main() {
	int b1, c1, b2, c2;
	scanf("%d%d%d%d", &b1, &c1, &b2, &c2);
	int x, y, d;
	d = exgcd(b1, b2, x, y);
	if ((c1 - c2) % d) {
		puts("NaN");
	} else {
		int t = (c1 - c2) / d;
		x *= t, y *= t;
		int g = b1 * b2 / d;
		int m = c2 + y * b2;
		int k = -m / g;
		if (k * g < -m) {
			k += 1;
		}
		printf("%d\n", k * g + m);
	}
	return 0;
}